What is the TRUE Source of My Unhappiness?

Hey all, no matter what I do, whether it's just simply try to be myself (whether it's saying or doing things I like doing), saying that I am letting go & moving on from past grudges with people that hurt me in the past (I decided that I was gonna let it go & move on), or whatever I do that was for trying to make me feel good on the outside, on the INSIDE it hurts. Whether I say & do stuff that I like or only saying & doing stuff that pleases certain people, I hurt inside & I feel apathetic throughout & depressed. Even though I decide that I let go of past grudges & move on, on the inside the pain Still lingers even though I said that I would just forgive, my mind never forgets and the pain hurts. Just about all the time I feel so depressed and apathetic even though I keep saying it will be better but it has not. There are so many factors that I do not know the true souce of my unhappiness. Can any of you help me out here.